Structure and biosynthetic assembly of gulmirecins, macrolide antibiotics from the predatory bacterium Pyxidicoccus fallax

A unique dual acyltransferase system shared in the polyketide chain initiation of kidamycinone and rubiflavinone biosynthesis

The pluramycin family of natural products has diverse substituents at the C2 position, which are closely related to their biological activity. Therefore, it is important to understand the biosynthesis of C2 substituents. In this study, we describe the biosynthesis of C2 moieties in Streptomyces sp. W2061, which produces kidamycin and rubiflavinone C-1, containing anthrapyran aglycones. Sequence analysis of the loading module (Kid13) of the PKS responsible for the synthesis of these anthrapyran aglycones is useful for confirming the incorporation of atypical primer units into the corresponding products. Kid13 is a ketosynthase-like decarboxylase (KSQ)-type loading module with unusual dual acyltransferase (AT) domains (AT1-1 and AT1-2). The AT1-2 domain primarily loads ethylmalonyl-CoA and malonyl-CoA for rubiflavinone and kidamycinone and rubiflavinone, respectively; however, the AT1-1 domain contributed to the functioning of the AT1-2 domain to efficiently load ethylmalonyl-CoA for rubiflavinone. We found that the dual AT system was involved in the production of kidamycinone, an aglycone of kidamycin, and rubiflavinone C-1 by other shared biosynthetic genes in Streptomyces sp. W2061. This study broadens our understanding of the incorporation of atypical primer units into polyketide products.

Myxobacteria: biology and bioactive secondary metabolites

Myxobacteria are Gram-negative eubacteria and they thrive in a variety of habitats including soil rich in organic matter, rotting wood, animal dung and marine environment. Myxobacteria are a promising source of new compounds associated with diverse bioactive spectrum and unique mode of action. The genome information of myxobacteria has revealed many orphan biosynthetic pathways indicating that these bacteria can be the source of several novel natural products. In this review, we highlight the biology of myxobacteria with emphasis on their habitat, life cycle, isolation methods and enlist all the bioactive secondary metabolites purified till date and their mode of action.

The potential of facultative predatory Actinomycetota spp. and prospects in agricultural sustainability

Actinomycetota in the phylum of bacteria has been explored extensively as a source of antibiotics and secondary metabolites. In addition to acting as plant growth-promoting agents, they also possess the potential to control various plant pathogens; however, there are limited studies that report the facultative predatory ability of Actinomycetota spp. Furthermore, the mechanisms that underline predation are poorly understood. We assessed the diversity of strategies employed by predatory bacteria to attack and subsequently induce the cell lysing of their prey. We revisited the diversity and abundance of secondary metabolite molecules linked to the different predation strategies by bacteria species. We analyzed the pros and cons of the distinctive predation mechanisms and explored their potential for the development of new biocontrol agents. The facultative predatory behaviors diverge from group attack "wolfpack," cell-to-cell proximity "epibiotic," periplasmic penetration, and endobiotic invasion to degrade host-cellular content. The epibiotic represents the dominant facultative mode of predation, irrespective of the habitat origins. The wolfpack is the second-used approach among the Actinomycetota harboring predatory traits. The secondary molecules as chemical weapons engaged in the respective attacks were reviewed. We finally explored the use of predatory Actinomycetota as a new cost-effective and sustainable biocontrol agent against plant pathogens.

Strategies to access biosynthetic novelty in bacterial genomes for drug discovery

Bacteria provide a rich source of natural products with potential therapeutic applications, such as novel antibiotic classes or anticancer drugs. Bioactivity-guided screening of bacterial extracts and characterization of biosynthetic pathways for drug discovery is now complemented by the availability of large (meta)genomic collections, placing researchers into the postgenomic, big-data era. The progress in next-generation sequencing and the rise of powerful computational tools provide unprecedented insights into unexplored taxa, ecological niches and 'biosynthetic dark matter', revealing diverse and chemically distinct natural products in previously unstudied bacteria. In this Review, we discuss such sources of new chemical entities and the implications for drug discovery with a particular focus on the strategies that have emerged in recent years to identify and access novelty.

Myxobacteria as a Source of New Bioactive Compounds: A Perspective Study

Myxobacteria are unicellular, Gram-negative, soil-dwelling, gliding bacteria that belong to class δ-proteobacteria and order Myxococcales. They grow and proliferate by transverse fission under normal conditions, but form fruiting bodies which contain myxospores during unfavorable conditions. In view of the escalating problem of antibiotic resistance among disease-causing pathogens, it becomes mandatory to search for new antibiotics effective against such pathogens from natural sources. Among the different approaches, Myxobacteria, having a rich armor of secondary metabolites, preferably derivatives of polyketide synthases (PKSs) along with non-ribosomal peptide synthases (NRPSs) and their hybrids, are currently being explored as producers of new antibiotics. The Myxobacterial species are functionally characterized to assess their ability to produce antibacterial, antifungal, anticancer, antimalarial, immunosuppressive, cytotoxic and antioxidative bioactive compounds. In our study, we have found their compounds to be effective against a wide range of pathogens associated with the concurrence of different infectious diseases.

Total Synthesis and Bioactivity Mapping of Geodiamolide H

The first total synthesis of the actin-stabilizing marine natural product geodiamolide H was achieved. Solid-phase based peptide assembly paired with scalable stereoselective syntheses of polyketide building blocks and an optimized esterification set the stage for investigating the key ring-closing metathesis. Geodiamolide H and synthetic analogues were characterized for their toxicity and for antiproliferative effects in cellulo, by characterising actin polymerization induction in vitro, and by docking on the F-actin target and property computation in silico, for a better understanding of structure-activity relationships (SAR). A non-natural analogue of geodiamolide H was discovered to be most potent in the series, suggesting significant potential for tool compound design.

Assessment of Evolutionary Relationships for Prioritization of Myxobacteria for Natural Product Discovery

Discoveries of novel myxobacteria have started to unveil the potentially vast phylogenetic diversity within the family Myxococcaceae and have brought about an updated approach to myxobacterial classification. While traditional approaches focused on morphology, 16S gene sequences, and biochemistry, modern methods including comparative genomics have provided a more thorough assessment of myxobacterial taxonomy. Herein, we utilize long-read genome sequencing for two myxobacteria previously classified as Archangium primigenium and Chondrococcus macrosporus, as well as four environmental myxobacteria newly isolated for this study. Average nucleotide identity and digital DNA-DNA hybridization scores from comparative genomics suggest previously classified as A. primigenium to instead be a novel member of the genus Melittangium, C. macrosporus to be a potentially novel member of the genus Corallococcus with high similarity to Corallococcus exercitus, and the four isolated myxobacteria to include another novel Corallococcus species, a novel Pyxidicoccus species, a strain of Corallococcus exiguus, and a potentially novel Myxococcus species with high similarity to Myxococcus stipitatus. We assess the biosynthetic potential of each sequenced myxobacterium and suggest that genus-level conservation of biosynthetic pathways support our preliminary taxonomic assignment. Altogether, we suggest that long-read genome sequencing benefits the classification of myxobacteria and improves determination of biosynthetic potential for prioritization of natural product discovery.

A Synthesis Strategy for the Production of a Macrolactone of Gulmirecin A via a Ni(0)-Mediated Reductive Cyclization Reaction

A synthesis strategy for the production of a key synthetic intermediate of gulmirecin A was described. The key reaction in the preparation of the 12-membered macrolactone is the Ni(0)-mediated reductive cyclization reaction of ynal using an N-heterocyclic carbene ligand and silane reductant. In addition, the α-selective glycosylation reaction of the macrolactone was performed to demonstrate the synthesis of gulmirecin and disciformycin precursors.

Marine Actinobacteria: Screening for Predation Leads to the Discovery of Potential New Drugs against Multidrug-Resistant Bacteria

Predatory bacteria constitute a heterogeneous group of prokaryotes able to lyse and feed on the cellular constituents of other bacteria in conditions of nutrient scarcity. In this study, we describe the isolation of Actinobacteria predator of other bacteria from the marine water of the Moroccan Atlantic coast. Only 4 Actinobacteria isolates showing strong predation capability against native or multidrug-resistant Gram-positive or Gram-negative bacteria were identified among 142 isolated potential predatory bacteria. These actinobacterial predators were shown to belong to the Streptomyces genus and to inhibit the growth of various native or multidrug-resistant micro-organisms, including Micrococcus luteus, Staphylococcus aureus (native and methicillin-resistant), and Escherichia coli (native and ampicillin-resistant). Even if no clear correlation could be established between the antibacterial activities of the selected predator Actinobacteria and their predatory activity, we cannot exclude that some specific bio-active secondary metabolites were produced in this context and contributed to the killing and lysis of the bacteria. Indeed, the co-cultivation of Actinobacteria with other bacteria is known to lead to the production of compounds that are not produced in monoculture. Furthermore, the production of specific antibiotics is linked to the composition of the growth media that, in our co-culture conditions, exclusively consisted of the components of the prey living cells. Interestingly, our strategy led to the isolation of bacteria with interesting inhibitory activity against methicillin-resistant S. aureus (MRSA) as well as against Gram-negative bacteria.

Screening for inhibitors of mutacin synthesis in Streptococcus mutans using fluorescent reporter strains

Background

Within the polymicrobial dental plaque biofilm, bacteria kill competitors by excreting mixtures of bacteriocins, resulting in improved fitness and survival. Inhibiting their bacteriocin synthesis might therefore be a useful strategy to eliminate specific pathogens. We used Streptococcus mutans, a highly acidogenic inhabitant of dental plaque, as a model and searched for natural products that reduced mutacin synthesis. To this end we fused the promoter of mutacin VI to the GFP+ gene and integrated the construct into the genome of S. mutans UA159 by single homologous recombination.

Results

The resulting reporter strain 423p - gfp + was used to screen 297 secondary metabolites from different sources, mainly myxobacteria and fungi, for their ability to reduce the fluorescence of the fully induced reporter strain by > 50% while growth was almost unaffected (> 90% of control). Seven compounds with different chemical structures and different modes of action were identified. Erinacine C was subsequently validated and shown to inhibit transcription of all three mutacins of S. mutans. The areas of the inhibition zones of the sensor strains S. sanguinis and Lactococcus lactis were reduced by 35% to 61% in comparison to controls in the presence of erinacine C, demonstrating that the amount of active mutacins in the culture supernatants of S. mutans was reduced. Erinacines are cyathane diterpenes that were extracted from cultures of the edible mushroom Hericium erinaceus. They have anti-inflammatory, antimicrobial and neuroprotective effects. For erinacine C, a new biological activity was found here.

Conclusions

We demonstrate the successful development of a whole-cell fluorescent reporter for the screening of natural compounds and report that erinacine C suppresses mutacin synthesis in S. mutans without affecting cell viability.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1170-3) contains supplementary material, which is available to authorized users.

Myxobacterial natural products: An under-valued source of products for drug discovery for neurological disorders

Age-related disorders impose noticeable financial and emotional burdens on society. This impact is becoming more prevalent with the increasing incidence of neurodegenerative diseases and is causing critical concerns for treatment of patients worldwide. Parkinson's disease, Alzheimer's disease, multiple sclerosis and motor neuron disease are the most prevalent and the most expensive to treat neurodegenerative diseases globally. Therefore, exploring effective therapies to overcome these disorders is a necessity. Natural products and their derivatives have increasingly attracted attention in drug discovery programs that have identified microorganisms which produce a large range of metabolites with bioactive properties. Myxobacteria, a group of Gram-negative bacteria with large genome size, produce a wide range of secondary metabolites with significant chemical structures and a variety of biological effects. They are potent natural product producers. In this review paper, we attempt to overview some secondary metabolites synthesized by myxobacteria with neuroprotective activity through known mechanisms including production of polyunsaturated fatty acids, reduction of apoptosis, immunomodulation, stress reduction of endoplasmic reticulum, stabilization of microtubules, enzyme inhibition and serotonin receptor modulation.

Herpetopanone, a diterpene from Herpetosiphon aurantiacus discovered by isotope labeling

The genome of the predatory bacterium Herpetosiphon aurantiacus 114-95^T harbors a number of biosynthesis genes, including four terpene cyclase genes. To identify the terpenes biosynthesized from H. aurantiacus 114-95^T, we fed the strain with ¹³C-labeled glucose and, subsequently, searched for characteristic mass shifts in its metabolome. This approach led to the discovery of a new natural product, of which the isotope pattern is indicative for a diterpene originating from the methylerythritol phosphate pathway. After large-scale fermentation of H. aurantiacus 114-95^T, the putative diterpene was isolated in sufficient quantity to enable NMR-based structure elucidation. The compound, for which the name herpetopanone is proposed, features a rare octahydro-1H-indenyl skeleton. Herpetopanone bears resemblance to cadinane-type sesquiterpenes from plants, but is structurally entirely unprecedented in bacteria. Based on its molecular architecture, a possible biosynthetic pathway is postulated.

Antimicrobial discovery inspired by ecological interactions

Bacteria represent an unparalleled source of antibiotics used to treat infectious diseases. Yet, genome analyses have revealed that their full biosynthetic potential is much larger than expected. Valuable strategies to unearth hidden antibiotics are genome mining, pathway engineering and triggering, as well as co-cultivation approaches. Nevertheless, there is growing understanding that it is often essential to consider the ecological context and that there is a great potential for antimicrobial discovery from bacteria engaged in well-defined interactions with other organisms. Various ecological scenarios involving antimicrobial agents are outlined in this review: predator-prey and pathogenic interactions, the protection of insect assets such as offspring and cultivars, as well as host protection in symbiotic relationships with plants, invertebrates and animals/humans. The illustrative examples given reinforce the idea that examination of interactions between organisms can yield new antimicrobial compounds, and ultimately further our understanding of the function of these molecules in the environment.

Myxobacteria Are Able to Prey Broadly upon Clinically-Relevant Pathogens, Exhibiting a Prey Range Which Cannot Be Explained by Phylogeny

Myxobacteria are natural predators of microorganisms and the subjects of concerted efforts to identify novel antimicrobial compounds. Myxobacterial predatory activity seems to require more than just the possession of specific antimicrobial metabolites. Thus a holistic approach to studying predation promises novel insights into antimicrobial action. Here, we report the isolation of 113 myxobacteria from samples of soil taken from a range of habitats in mid Wales. Predatory activity of each isolate was quantified against a panel of clinically important prey organisms, including Klebsiella pneumoniae, Proteus mirabilis, Candida albicans, Enterococcus faecalis, and three species of Staphylococcus. Myxobacterial isolates exhibited a wide range of predation activity profiles against the panel of prey. Efficient predation of all prey by isolates within the collection was observed, with K. pneumoniae and C. albicans proving particularly susceptible to myxobacterial predation. Notably efficient predators tended to be proficient at predating multiple prey organisms, suggesting they possess gene(s) encoding a broad range killing activity. However, predatory activity was not congruent with phylogeny, suggesting prey range is subject to relatively rapid specialization, potentially involving lateral gene transfer. The broad but patchy prey ranges observed for natural myxobacterial isolates also implies multiple (potentially overlapping) genetic determinants are responsible for dictating predatory activity.

Herpetosiphon gulosus sp. nov., a filamentous predatory bacterium isolated from sandy soil and Herpetosiphon giganteus sp. nov., nom. rev

Three filamentous gliding bacteria from the German Collection of Microorganisms and Cell Cultures, Hp g11, Hp g471 and Hp g472, were subjected to a phylogenetic analysis. These organisms had previously been classified as members of the genus Herpetosiphon based on their growth physiology and morphology. However, a taxonomic assignment at the species level had not been carried out. Analysis of 16S rRNA sequences now confirmed the close relationship of strain Hp g472 to Herpetosiphon aurantiacus DSM 785T (98.6 % nucleotide identity) and Herpetosiphon geysericola DSM 7119T (97.7 %). The results of DNA-DNA hybridization experiments further implied that strain Hp g472 should be classified as a distinct species. The DNA G+C content of strain Hp g472 was 49.9 mol%. The major quinone was MK-10 and the predominant cellular fatty acids were C18 : 1, C16 : 1 and C16 : 0. Based on phenotypic, chemotaxonomic and phylogenetic data it was concluded that strain Hp g472 represents a novel species of the genus Herpetosiphon, for which the name Herpetosiphon gulosus sp. nov. is proposed. The type strain is Hp g472T (=DSM 52871T=NBRC 112829T). In contrast to Hp g472T, the strains Hp g11 and Hp g471 exhibited closest 16S rRNA gene sequence similarity (>99 %) with 'Herpetosiphon giganteus' Hp a2. The distinctive genotypic and phenotypic properties of the latter supported the revival of the name as Herpetosiphon giganteus (ex Reichenbach & Golecki, 1975) sp. nov., nom. rev. We propose the previously deposited reference strain DSM 589T=NBRC 112828T as the type strain.

Antibiotics from Gram-negative bacteria: a comprehensive overview and selected biosynthetic highlights

Covering: up to 2017The overwhelming majority of antibiotics in clinical use originate from Gram-positive Actinobacteria. In recent years, however, Gram-negative bacteria have become increasingly recognised as a rich yet underexplored source of novel antimicrobials, with the potential to combat the looming health threat posed by antibiotic resistance. In this article, we have compiled a comprehensive list of natural products with antimicrobial activity from Gram-negative bacteria, including information on their biosynthetic origin(s) and molecular target(s), where known. We also provide a detailed discussion of several unusual pathways for antibiotic biosynthesis in Gram-negative bacteria, serving to highlight the exceptional biocatalytic repertoire of this group of microorganisms.

Molecular and functional characterization of myxobacteria isolated from soil in India

This study reports the isolation of myxobacteria from soil collected from plains in north India. Based on the morphology and 16S rDNA sequence, the isolated myxobacteria were identified as Corallococcus sp., Pyxidicoccus sp., Myxococcus sp., Cystobacter sp. and Archangium sp. The myxobacteria were functionally characterized to assess their ability to produce antibacterial and anticancer metabolites. The isolates were found to be functionally versatile as they produced extracellular bioactive molecules that exhibited high frequency of activities against Bacillus cereus, Mycobacterium smegmatis, Enterobacter cloacae and Pseudomonas syringae. The strains also showed cytotoxic activity against the human cancer cell lines of liver, pancreas, prostrate, bone and cervix. These results indicate the importance of isolating diverse strains of myxobacteria from unexplored habitats to find novel bioactive compounds. Moreover, the bioactive molecules explored in this study are predominantly hydrophilic compounds, obviating the limitations of solubility-related aspect of drug discovery.

The Uncommon Enzymology of Cis-Acyltransferase Assembly Lines

The enzymology of 135 assembly lines containing primarily cis-acyltransferase modules is comprehensively analyzed, with greater attention paid to less common phenomena. Diverse online transformations, in which the substrate and/or product of the reaction is an acyl chain bound to an acyl carrier protein, are classified so that unusual reactions can be compared and underlying assembly-line logic can emerge. As a complement to the chemistry surrounding the loading, extension, and offloading of assembly lines that construct primarily polyketide products, structural aspects of the assembly-line machinery itself are considered. This review of assembly-line phenomena, covering the literature up to 2017, should thus be informative to the modular polyketide synthase novice and expert alike.

Natural products from myxobacteria: novel metabolites and bioactivities

Covering: 2011-July 2016Myxobacteria are a rich source for structurally diverse secondary metabolites with intriguing biological activities. Here we report on new natural products that were isolated from myxobacteria in the period of 2011 to July 2016. Some examples of recent advances on modes-of-action are also summarised along with a more detailed overview on five compound classes currently assessed in preclinical studies.

Zincophorin - biosynthesis in Streptomyces griseus and antibiotic properties

Zincophorin is a polyketide antibiotic that possesses potent activity against Gram-positive bacteria, including human pathogens. While a number of total syntheses of this highly functionalized natural product were reported since its initial discovery, the genetic basis for the biosynthesis of zincophorin has remained unclear. In this study, the co-linearity inherent to polyketide pathways was used to identify the zincophorin biosynthesis gene cluster in the genome of the natural producer Streptomyces griseus HKI 0741. Interestingly, the same locus is fully conserved in the streptomycin-producing actinomycete S. griseus IFO 13350, suggesting that the latter bacterium is also capable of zincophorin biosynthesis. Biological profiling of zincophorin revealed a dose-dependent inhibition of the Gram-positive bacterium Streptococcus pneumoniae. The antibacterial effect, however, is accompanied by cytotoxicity. Antibiotic and cytotoxic activities were completely abolished upon esterification of the carboxylic acid group in zincophorin.

Unraveling the predator-prey relationship of Cupriavidus necator and Bacillus subtilis

Cupriavidus necator is a non-obligate bacterial predator of Gram-negative and Gram-positive bacteria. In this study, we set out to determine the conditions, which are necessary to observe predatory behavior of C. necator. Using Bacillus subtilis as a prey organism, we confirmed that the predatory performance of C. necator is correlated with the available copper level, and that the killing is mediated, at least in part, by secreted extracellular factors. The predatory activity depends on the nutrition status of C. necator, but does not require a quorum of predator cells. This suggests that C. necator is no group predator. Further analyses revealed that sporulation enables B. subtilis to avoid predation by C. necator. In contrast to the interaction with predatory myxobacteria, however, an intact spore coat is not required for resistance. Instead resistance is possibly mediated by quiescence.

Diversity of Natural Product Biosynthetic Genes in the Microbiome of the Deep Sea Sponges Inflatella pellicula, Poecillastra compressa, and Stelletta normani

Three different deep sea sponge species, Inflatella pellicula, Poecillastra compressa, and Stelletta normani comprising seven individual samples, retrieved from depths of 760–2900 m below sea level, were investigated using 454 pyrosequencing for their secondary metabolomic potential targeting adenylation domain and ketosynthase domain sequences. The data obtained suggest a diverse microbial origin of nonribosomal peptide synthetases and polyketide synthase fragments that in part correlates with their respective microbial community structures that were previously described and reveals an untapped source of potential novelty. The sequences, especially the ketosynthase fragments, display extensive clade formations which are clearly distinct from sequences hosted in public databases, therefore highlighting the potential of the microbiome of these deep sea sponges to produce potentially novel small-molecule chemistry. Furthermore, sequence similarities to gene clusters known to be involved in the production of many classes of antibiotics and toxins including lipopeptides, glycopeptides, macrolides, and hepatotoxins were also identified.

Variochelins, Lipopeptide Siderophores from Variovorax boronicumulans Discovered by Genome Mining

Photoreactive siderophores have a major impact on the growth of planktonic organisms. To date, these molecules have mainly been reported from marine bacteria, although evidence is now accumulating that some terrestrial bacteria also harbor the biosynthetic potential for their production. In this paper, we describe the genomics-driven discovery and characterization of variochelins, lipopeptide siderophores from the bacterium Variovorax boronicumulans, which thrives in soil and freshwater habitats. Variochelins are different from most other lipopeptide siderophores in that their biosynthesis involves a polyketide synthase. We demonstrate that the ferric iron complex of variochelin A possesses photoreactive properties and present the MS-derived structures of two degradation products that emerge upon light exposure.

Antibiotics from predatory bacteria

Bacteria, which prey on other microorganisms, are commonly found in the environment. While some of these organisms act as solitary hunters, others band together in large consortia before they attack their prey. Anecdotal reports suggest that bacteria practicing such a wolfpack strategy utilize antibiotics as predatory weapons. Consistent with this hypothesis, genome sequencing revealed that these micropredators possess impressive capacities for natural product biosynthesis. Here, we will present the results from recent chemical investigations of this bacterial group, compare the biosynthetic potential with that of non-predatory bacteria and discuss the link between predation and secondary metabolism.

Harnessing Enzymatic Promiscuity in Myxochelin Biosynthesis for the Production of 5-Lipoxygenase Inhibitors

The siderophore myxochelin A is a potent inhibitor of human 5-lipoxygenase (5-LO). To clarify whether the iron-chelating properties of myxochelin A are responsible for this activity, several analogues of this compound were generated in the native producer Pyxidicoccus fallax by precursor-directed biosynthesis. Testing in a cell-free assay unveiled three derivatives with bioactivity comparable with that of myxochelin A. Furthermore, it became evident that inhibition of 5-LO by myxochelins does not correlate with their iron affinities.

Quantitative Analysis of Lysobacter Predation

Bacteria of the genus Lysobacter are considered to be facultative predators that use a feeding strategy similar to that of myxobacteria. Experimental data supporting this assumption, however, are scarce. Therefore, the predatory activities of three Lysobacter species were tested in the prey spot plate assay and in the lawn predation assay, which are commonly used to analyze myxobacterial predation. Surprisingly, only one of the tested Lysobacter species showed predatory behavior in the two assays. This result suggested that not all Lysobacter strains are predatory or, alternatively, that the assays were not appropriate for determining the predatory potential of this bacterial group. To differentiate between the two scenarios, predation was tested in a CFU-based bioassay. For this purpose, defined numbers of Lysobacter cells were mixed together with potential prey bacteria featuring phenotypic markers, such as distinctive pigmentation or antibiotic resistance. After 24 h, cocultivated cells were streaked out on agar plates and sizes of bacterial populations were individually determined by counting the respective colonies. Using the CFU-based predation assay, we observed that Lysobacter spp. strongly antagonized other bacteria under nutrient-deficient conditions. Simultaneously, the Lysobacter population was increasing, which together with the killing of the cocultured bacteria indicated predation. Variation of the predator/prey ratio revealed that all three Lysobacter species tested needed to outnumber their prey for efficient predation, suggesting that they exclusively practiced group predation. In summary, the CFU-based predation assay not only enabled the quantification of prey killing and consumption by Lysobacter spp. but also provided insights into their mode of predation.

Myxochelins target human 5-lipoxygenase

Extracts of the predatory myxobacterium Pyxidicoccus fallax HKI 727 showed antiproliferative effects on leukemic K-562 cells. Bioactivity-guided fractionation led to the isolation of the bis-catechol myxochelin A and two new congeners. The biosynthetic origin of myxochelins C and D was confirmed by feeding studies with isotopically labeled precursors. Pharmacological testing revealed human 5-lipoxygenase (5-LO) as a molecular target of the myxochelins. In particular, myxochelin A efficiently inhibited 5-LO activity with an IC50 of 1.9 μM and reduced the proliferation of K-562 cells at similar concentrations.